Friday, February 24, 2012

First Civilization Part 1 Chapter 5

 

Based on orbital observations and the examination of the Martian meteorite collection, the surface of Mars appears to be composed primarily of basalt. Basaltic rock is a black volcanic rock containing 55%  silicon dioxide .  Minerals found in balsaltic andesite include olivine, augite, and plagioclase. 

basaltic-andesite

Basaltic andesite

Some evidence suggests that a portion of the Martian surface is more silica-rich than typical basalt, and may be similar to andesitic rocks (A gray, fine-grained volcanic rock. Andesite consists mainly of sodium-rich plagioclase and one or more mafic minerals such as biotite, hornblende, or pyroxene. Plagioclase is a member of the feldspar family. 

Basaltic andiosite plagioglase

Basaltic andesite plagioclase

It is a major mineral in the Earth's crust and the rocky highlands of the Earth's moon.   It often contains small, visible crystals (phenocrysts) of plagioclase in it, these observations may also be explained by silicon dioxide (sand).  These are igneous rocks and are the result of the cooling and solidification of magma or lava.
Crater density timescale:
Studies of impact crater densities on the Martian surface have delineated four broad periods in the planet's geologic history. The periods were named after places on Mars that have large-scale surface features, such as large craters or widespread lava flows that date back to these time periods. There is also a second method called the Mineral Time Scale. The Crater Density Timescale is as follows:

CraterTimeline

Pre-Noachian: Represents the interval from the accretion and differentiation of the planet about 4.5 billion years ago (Gya) to the formation of the Hellas impact basin, between 4.1 and 3.8 Gya. Most of the geologic record of this interval has been erased by subsequent erosion and high impact rates. The crustal dichotomy (or shore of the Northern Ocean) is thought to have formed during this time, along with the Argyre and Isidis basins.
Noachian Period:  (named after Noachis Terra): Formation of the oldest extant surfaces of Mars, 4.5 billion years ago to 3.5 billion years ago. Noachian age surfaces are scarred by many large impact craters. The Tharsis bulge, a volcanic upland, is thought to have formed during this period (which means volcano activity had begun), with extensive flooding by liquid water late in the period.

tharsis bulge area

Tharsis Bulge Area

Hesperian Period:  (named after Hesperia Plenum): 3.5 billion years ago to 2.9 billion years ago. The Hesperian period is marked by the formation of extensive lava plains on Mars.
Amazonian Period: (named after Amazonis Planitia): 3.3-2.9 billion years ago to present. Amazonian regions have few meteorite impact craters, but are otherwise quite varied. Olympus Mons formed during this period, along with lava flows elsewhere on Mars which means volcano activity had increased.  First life appears on Mars.

mars-sea2

Martian river leading to the Northern Ocean

 

Mineral Time scale:
In 2006, researchers using data from the OMEGA Visible and Infrared Mineralogical Mapping Spectrometer on board the Mars Express orbiter proposed an alternative Martian timescale based on the predominant type of mineral alteration that occurred on Mars due to different types of chemical weathering in the planets' past. They proposed dividing the history of the Mars into three eras- the Phyllocian, Theiikian and Siderikan:
mineral timeline
Phyllocian Period: (named after phyllosilicate or clay minerals that characterize the era) lasted from the formation of the planet until around the Early Noachian (about 4.0 Gya). OMEGA identified outcropping of phyllosilicates at numerous locations on Mars, all in rocks that were exclusively Pre-Noachian or Noachian in age (most notably in rock exposures in Nili Fossae and Mawrith Vallis):
clay minerals on Mars

Clay minerals on Mars suggest the presence of liquid water in large quantities.

Clay or Phyllosillicates require a water-rich, alkaline environment to form. The Phyllocian era correlates with the age of valley network formation on Mars, suggesting an early climate that was conducive to the presence of abundant surface water. It is thought that deposits from this era are the best candidates in which to search for evidence of past and present life on the planet.
Theiikian Period: (named after sulfurous in Greek, for the sulfate minerals that were formed) lasted until about 3.5 Gya. It was an era of extensive volcanism, which released large amounts of sulfur dioxide  into the atmosphere. The  sulfur dioxide combined with water to create a sulfuric acid-rich environment that allowed the formation of hydrated sulfates (notably kieserite and gypsum).
Siderikan Period:  (named for iron in Greek, for the iron oxides that formed) lasted from 3.5 Gya until the present. Simple life forms and animals appear and go underground with the decline of volcanism and lack of available water late in that period. The most notable surface weathering process has been the slow oxidation of the iron-rich rocks by atmospheric peroxides producing the red iron oxides that give the planet its familiar color.


Earth Equivalent: Almost all this latter time can be located in the Proterozoic era 2.5 billion years-512 Ma. The Atmosphere became oxygen and rich and simple life forms appear.  1.5 Gya-251 Ma. multicultural life and first animals appear.  In 380 Ma first vertebrae land animals appear. Melezoic-Cenozoic:  251-65 Ma Age of the dinosaurs:
trex-triceratops